Anorexia Nervosa Dampens Subjective and Facial Pain Responsiveness

TL;DR

People with anorexia nervosa show reduced facial expressions of pain, even though their subjective pain levels are similar to healthy individuals.

Contribution

This study is the first to show that anorexia nervosa patients have reduced facial pain expressions independent of subjective pain reports.

Findings

AN patients showed significantly reduced facial expressions of pain compared to healthy controls.

The reduction in facial pain expression was not explained by differences in pain thresholds, ratings, eating pathology, or depression.

This suggests impaired communication of pain in AN on both verbal and nonverbal levels.

Abstract

Background/Objectives: Individuals with anorexia nervosa (AN) are known to exhibit both reduced pain sensitivity—when assessed via thresholds and subjective ratings—and diminished facial expressions of emotion. Therefore, investigating the facial response to pain in this population is of particular interest. Method: Seventeen patients with AN and 18 age- and sex-matched healthy controls were assessed using a thermode to induce heat pain. Subjective pain measures included pain threshold, pain tolerance, and pain ratings of supra-threshold stimuli, rated on a numerical rating scale (NRS). Facial responses to the suprathreshold stimuli were analyzed using the Facial Action Coding System (FACS). Eating pathology was assessed using the Eating Attitudes Test (EAT-26), the Eating Disorder Inventory-2 (EDI-2) and the body mass index (BMI), while depression was measured using the Beck Depression Inventory-II (BDI-II). Results: Compared with healthy controls, AN patients showed altogether significantly reduced facial expressions of pain, with particularly pronounced reductions in Action Units AU 6_7 and AU 9_10. In contrast, subjective pain measures showed only marginal differences between groups. Importantly, the reduction in facial expression could not be accounted for by differences in pain thresholds or ratings, nor by levels of eating pathology or depression. Conclusions: Individuals with AN display a markedly reduced facial expression of pain, which was observed for the first time, consistent with similar findings regarding the facial expressions of emotions. As this reduction cannot be explained by subjective pain report, it suggests that the communication of pain is impaired on two levels in AN: both in verbal and in nonverbal signaling. This may hinder the ability of others to recognize and respond to their pain appropriately.

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